Al-Shabab militants have launched an attack on the main African Union military base near Mogadishu airport in Somalia.

Explosions and gunfire could be heard in the vicinity, AU spokesman Col Ali Houmed told AFP.

Al-Shabab has claimed responsibility for the attack and says its fighters are inside the base.

The African Union has over 20,000 troops in the country to help the weak government battle al-Shabab.

Sheikh Abdiasis Abu Musab, al-Shabab's military spokesman, said that fighters had breached the compound's defences.

"Our fighters have entered AU's Halane base by force through the gate and now fighting is going on inside the base," he said.

The AU base is on the edge of the compound of Mogadishu's international airport.

The base also hosts the British and Italian embassies and is used as the headquarters for United Nations operations in Somalia.

Aleem Siddique, a UN spokesman in Somalia, told Reuters news agency that all UN staff were safe.

Earlier in December, at least six people were killed when al-Shabab attacked a UN convoy near the airport.

Various armed groups have been battling for control of Somalia since the overthrow of President Siad Barre in 1991.